The present invention relates to a device and a method for controlling at least one vehicle motion quantity which describes a motion of a vehicle.
A device for controlling at least one vehicle motion quantity is described in an article published in the journal Automobiltechnische Zeitschrift (ATZ), 96, 1994, Vol. 11, pp. 674 to 689 xe2x80x9cFDRxe2x80x94Die Fahrdynamikregelung von Boschxe2x80x9d (FDRxe2x80x94vehicle dynamics control by Bosch). The vehicle motion quantity here is the yaw rate of the vehicle. In order to control the vehicle""s yaw rate, the measured yaw rate is compared to a yaw rate setpoint value. In making this comparison, the system deviation of the yaw rate is determined and driver-independent, wheel-individual brake interventions and/or engine interventions are performed as a function of this system deviation. Using this brake intervention, primarily a yaw moment is applied to the vehicle to bring the actual yaw rate closer to the setpoint yaw rate.
The contents of the above-mentioned ATZ article are hereby included in the present application.
The above-described vehicle dynamics control also generally known as ESP (Electronic Stability Program) was initially developed for highway vehicles, but it is now being increasingly used in off-road-capable vehicles. However, undesirable interventions by the vehicle controller with which the yaw rate of the vehicle is to be controlled are disturbing in off-road situations. Thus, one object of the present invention is to modify existing devices for controlling at least one vehicle motion quantity, in particular the yaw rate of the vehicle, so that it can also be used in off-road-capable vehicles.
German Published Patent Application No. 39 33 652 describes an antilock control system and a traction control system suitable for driving on off-road terrain. The antilock control system contains sensors for determining the wheel speeds. A vehicle deceleration is determined from the wheel speeds in an analyzer circuit. Signals of a vehicle deceleration sensor are also processed in the analyzer circuit. The vehicle deceleration determined from the wheel speeds, and the signals of the vehicle deceleration sensor are compared to one another. If the measured vehicle deceleration predominates, the ABS control is modified toward less sensitive braking. A similar procedure is used in the traction control system.
Furthermore, German Published Patent Application No. 195 44 445 describes a method for improving the control response of an antilock control system for off-road vehicles. In order to improve the control response of the antilock control system for off-road vehicles, the control is configured for a vehicle reference velocity that is less than a predefined velocity limit value so that the antilock control for the second wheel of the axle is not initiated until one wheel of an axle is locked. Thus basically only one wheel of an axle is allowed to lock for low velocities. Furthermore, the control can also be configured so that a special control mode is activated when off-road driving and low vehicle velocity are detected.
The devices described in the two above-mentioned documents relate to devices for controlling a quantity describing the wheel behavior, namely the wheel slip. In other words, using these devices the wheel behavior is adjusted according to a control algorithm i.e., the wheel behavior or the vehicle motion is controlled. The control of a vehicle motion quantity which describes a motion of the vehicle, for example, the rotation of the vehicle about its vertical axis is not possible using these devices because the wheel information does not provide indications concerning the vehicle motion and, in addition, these devices do not to detect any quantity through which specific information concerning the vehicle motion can be made available and which is used in the control as a control quantity. In the case of the off-road-capable brake slip controller or traction controller from the related art, the wheel slip has the primary function in the control, i.e., the wheel is stabilized by interventions which originate in the control. The vehicle motion in this case is initially of secondary importance.
On the other hand, in controlling a vehicle motion, the vehicle motion is of primary importance for the control, i.e., the vehicle is stabilized. The behavior of the wheels during this control is initially of secondary importance.
The device according to the present invention is a device for controlling at least one vehicle motion quantity which describes a motion of a vehicle. The device contains a control arrangement for activating actuators to control the vehicle motion quantity. In addition, the device contains a determining arrangement for determining a poor road stretch quantity which describes the travel of the vehicle on a poor road stretch. The control arrangement is affected as a function of the poor road stretch quantity so that the sensitivity of the control arrangement is adapted to the travel of the vehicle on a poor road stretch.
The control arrangement contained in the device according to the present invention are composed of one higher-level and at least one lower-level controller. According to the present invention, both controllers are affected as a function of the poor road stretch quantity.
The higher-level controller is a controller for controlling a transverse dynamics quantity which describes the transverse dynamics of the vehicle. This controller is used to perform at least driver-independent wheel-individual brake interventions as soon as a deviation quantity which describes the deviation between an actual value and a setpoint value for the transverse dynamics quantity exceeds a control threshold. The transverse dynamics quantity is a quantity which describes the yaw rate of the vehicle. According to the present invention, the control threshold of the higher-level controller is increased as a function of the poor road stretch quantity.
When the vehicle travels on a poor road stretch, i.e. in off-road situations as may be the case in track grooves or on gravel roads, for example, greater deviations between the actual value and the setpoint value of the transverse dynamics quantity may occur without control intervention being necessary. For this reason, the control threshold of the higher-level controller is increased and thus the higher level controller is made less sensitive.
When the vehicle travels on a poor road stretch, driver-independent wheel-individual brake interventions performed to control the at least one vehicle motion quantity are suppressed or reduced in their frequency or intensity compared to the situation where the vehicle travels on a non-poor road stretch by affecting the higher-level controller. Consequently no disturbing intervention occurs when the vehicle travels on a poor road stretch.
The at least one lower-level controller is advantageously a traction controller which is used to adjust the drive slip of the driven wheels according to a setpoint value for the drive slip. According to the present invention, the setpoint value for the drive slip is determined as a function of the poor road stretch quantity. Thus, sufficient traction is guaranteed by this measure when traveling on a poor road stretch.
When the vehicle travels on a poor road stretch, a greater drive torque or a greater drive slip is allowed on the driven wheels compared to the situation where the vehicle travels on a non-poor road stretch by affecting the at least one lower-level controller. When the vehicle travels on a poor road stretch, brake interventions and/or engine interventions performed to reduce the drive slip are suppressed or reduced in their frequency or intensity compared to the situation where the vehicle travels on a non-poor road stretch by affecting the at least one lower-level controller.
Advantageously, the setpoint value for the drive slip is advantageously composed of a first component which represents the desired traction and a second component which represents the required vehicle stability. Using a factor, it is determined which of the two components has a greater weight in the setpoint value for the drive slip. According to the present invention, the first component is increased as a function of the poor road stretch quantity. As an alternative or additionally, the factor is affected as a function of the poor road stretch quantity so that the first component has a greater weight in the setpoint value for the drive slip than the second component.
Advantageously, a quantity which is a measure of the rate at which the engine torque delivered by the engine should be reduced is affected as a function of the poor road stretch quantity.
The poor road stretch quantity is advantageously determined as a function of wheel speed quantities which describe the wheel speeds of the individual wheels and of a velocity quantity which describes the velocity of the vehicle. A wheel oscillation quantity which is a measure of the wheel oscillations occurring when the vehicle travels on a poor road stretch is determined as a function of the wheel speed quantities. The poor road stretch quantity is determined as a function of this wheel oscillation quantity.
The poor road stretch quantity is advantageously a continuous quantity which assumes any desired value between a minimum value and a maximum value. In the case where the poor road stretch quantity assumes the minimum value, the control arrangement is not affected. In the case where the poor road stretch quantity assumes the maximum value, the control arrangement is affected to the maximum possible degree. In the case where the poor road stretch quantity assumes any desired value between the minimum and the maximum value, the control arrangement is continuously affected.
The wheel oscillation quantity is converted into a first continuous quantity which assumes a minimum value when the wheel oscillation quantity is less than a predefined first value and assumes a maximum value when the wheel oscillation quantity is greater than a predefined second value. The first continuous quantity increases continuously between the first and the second value for the wheel oscillation quantity. The velocity quantity is converted into a second continuous quantity which assumes a maximum value when the velocity quantity is less than a predefined first value and assumes a minimum value when the velocity quantity is greater than a predefined second value. The second continuous quantity decreases continuously between the first and the second value for the velocity quantity. The poor road stretch quantity is advantageously determined as the minimum of the first and the second continuous quantities.
The poor road stretch quantity is advantageously only determined when the off-road gear is selected in the case of vehicles equipped with a manual transmission that has a driver-selectable off-road gear.
In summary: the advantage of the device according to the present invention compared to the device described in the above-named ATZ article is that off-road situations, i.e., poor road stretches or travel on rough terrain are recognized and the control arrangement, i.e., the vehicle controller, is set to be less sensitive. Thus, both disturbing brake interventions and loss of traction are avoided. At the same time, the at least one vehicle motion quantity, i.e., the yaw rate of the vehicle, is controlled. In the case of the device described in the above-named ATZ article, disturbing brake interventions and also loss of traction may occur because the vehicle controller cannot be automatically set to be less sensitive in an off-road situation. This results in an uncomfortable driving sensation and is associated with noise. With the device described in the ATZ article, the driver can only press a passive button provided in the dashboard with which the vehicle controller is turned off (and on again) in order to prevent disturbing brake interventions and loss of traction. This, however, has the considerable disadvantage that in critical situations no more support by the controller is available.